Rietveld full-profile quantification of Portland cement clinker: The importance of including a full crystallography of the major phase polymorphs

Abstract

Crystalline phases present in the three NIST SRM Standard Portland cement clinkers 8486, 8487, and 8488 have been quantified from XRD powder patterns, (CoKα radiation), using the full-profile Rietveld method. Included in the Rietveld refinement are rhombohedral (R), monoclinic (M), and triclinic (T) crystal polymorphic forms of C3S, as well as crystal polymorphs of C2S and C3A. It is necessary to specify the phase crystallography including polymorphs, because of the extreme superposition of alite and belite XRD lines in the clinker patterns. Unsatisfactory results occur when only one or two of the C3S polymorphs are used in the Rietveld quantification; best results occur when all three polymorphs for C3S are included. The latter are called RMT-type refinements. The Rietveld full-profile XRD method is as precise as the microscope point-counting (MPC) method, but much less labor-intensive. The Rietveld method can quantify the C3S phase polymorphs, as well as total C3S. Rietveld and MPC methods give the same phase weight percentages for the three NIST standard clinkers. Calculated oxide weight percentages obtained from Rietveld phase weight percentages agree well with oxide percentages determined by XRF analysis. Bogue mineral weight percentages do not agree with Rietveld or MPC data, while transformation of the Bogue mineral percentages to oxides does not compare well with XRF analysis.